"Dr. Slick" wrote
From Pozar's Microwave Engineering (Pg. 606):

Reflection Coefficient looking into load = (Zl-Zo)/(Zl+Zo)

Where Zl is a purely real load impedance, and Zo is the
purely real characteristic impedance reference.

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Either Pozar (who I've never heard of) is not quite correct or Dr Slick has
misquoted him or taken him out of context.

In fact, the equation is also true for complex values of Zl and Zo. The
angle of RC can lie in any of the 4 quadrants. Furthermore, the magnitude of
RC can exceed unity.

I offer no references in support of this statement. It is issued here
entirely on my own responsibility.
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Reg, G4FGQ